Synchronizing circuit



Sept. 29, 1953 R. B. DOME SYNCHRONIZING CIRCUIT Filed Dec. 24, 1948Inventor Robert B. Dome, 3 m M His Attorney Patented Sept. 29, 1953syncnaomzmc. cmoUrr Robert B. Dome, Onondaga, N. Y.,' assignor toGeneral Electric Company, a corporation of New York Application December24, 1948, Serial No; 67,142

7 8 Claims.

My invention relates to synchronizing systems and, particularly, tosynchronizing systems which employ a periodic synchronizing signal whichmay be contaminated by spurious and undesired signals. While myinvention is of-general utility, it is of particular utility in thefield of television wherein it is desirable to provide.noise-freesynchronization of the scanning oscillators, especially theline frequency scanning oscillator, of the television receiver.

It is an object of my invention to provide means for synchronizing anoscillatorfrom a pcriodic synchronizing signal wherein the controlledoscillator is substantially unafiected by the presence of spurious noisepulses and random interference in the periodicsynchronizing signal.

For some purposes, it is necessary to synchronize an oscillator from aperiodically occurring pulse of small energy content relative to a sinewave of the same amplitude and frequency. This requirement is found intelevision systems wherein the composite synchronizing signal istransmitted as a series of pulses which occur during the line and fieldretrace intervals, these pulses being separated from the picture signalat the television receiver and utilized to synchronize the scanningoscillators at the receiver with the scanning oscillators at thetransmitter. Certain synchronizing systems heretofore proposedfor-synchronizing the scanning oscillators, at the receiver have appliedthe synchronizing signals directly to the scanning oscillators. Suchsystems provide relatively little discrimination against spurious pulseswhich may be interspersed-with the synchronizing ulses and hencesuchsystems are subject to periods of asynchronous operation. These directlysynchronizedoscillators will also fall out of synchronism immediatelyupon failure of synchronized pulses.

Various arrangementsvhave been proposed to obtain an automatic frequencycontrol or .AFC type of synchronization in which the synchronizingpulses are modified to a greater or. lesser extent before being appliedto the scanning oscillator, in order to provide discrimination againstrandom noise impulses. In these arrangements the synchronized pulses'are'combined with an output wave from the scanning oscillator, the waveshape of the resultant wave being a function of the relative. phaserelation of the syn-- chronizing pulses and the outputwave from'thescanning oscillator. The resultant wave is integrated over a largenumber. of cycles so that the effects of random noise pulses areaveraged out and only gradual changes in the phaserelationship of thetwo combined waves will appear in the output of the integration circuit.Certain of these arrangements,- whichare of the direct current controltype, utilize the direct current component of the above-m n ionedresultant wave for synchronization, the direct current componentbeingselected by means of a rectifier circuit and integrated by means of anelectrical circuit having a relatively long time constant. These directcurrent control systems usually require separate rectifiers andauxiliary ampliiiers to obtain a unidirectional control voltage ofsufllcient amplitude to control the scanning oscillator.

Other arrangements, recognizing that the alternating current componentsof the above-mentioned resultant wave are also dependent upon the phaserelationship of the two combined waves, utilize the alternatingcurrentcomponents of the resultant wave to effectsynchronization of thescanning oscillators. Inthese other arrangements, which employ an"alternating current control" type of synchronization, thealternating-current components of the resultant wave are selected andare integrated over a substantial number of cycles by storage in aresonant circuit which is tuned to'the' fundamental frequency of thealternating current components. Suchan alternating current controlsystem, forexample, is describedandclaim'ed in copendingapplicationSerialNo. 87,862 of Wolf J. Gruen, filed on Aprill6, 1949, now Patent2,598,370, granted May 27, 1952, and assigned to the assignee of thepresent invention. While the alternating current control system isadvantageous fromthe standpoint of simplicity, since the tank circuit ofthe scanning oscillator may itself be utilized to integrate thealternating current components, it is. desirable to increase thesynchronizing range of such a system without sacrificing the noisefreequalitiesiobtained thereby.

It is an object of my invention therefore to provide a new and improvedoscillator synchronizing system which eil'ects certain improvements overthe prior art systems of this nature.

It is another object of my invention to provide a new and improved meansfor synchronizing an oscillator from a periodic synchronizing signalwhich may be contaminated by spurious and undesired signals.

- It is still another object of my invention to provide a new andimproved means for synchro nizlng an oscillator from a periodicsynchronizing signal which may be contaminated by spurious and undesiredsignals, in which synchronization is effected by'means of thermalintegration of the periodic synchronizing signal.

It is a further object of my invention to provide a new and improvedmeans for synchronizing. an oscillator from a periodic synchronizingsignalwhichmay-be contaminated by spurious and undesired signals, inwhich synchronization is effected by means of thermal integration of thealternating current components of a waveform derivedfrom theperiodicqsynchronizing signal.

It is a still further object of my invention to provide a new andimproved means for synchronizating an oscillator from a periodicsynchronizing signal which may be contaminated by spurious and undesiredsignals, in which alternating current energy which is representative ofthe phase relationship of the periodic synchronizing signal and theoscillator, is stored in the form of heat energy in a heat dissipativebody, the average value of such stored heat energy being utilized tocontrol the frequency of the oscillator.

In accordanc with the invention, in my synchronized oscillator system asynchronizing signal consisting of periodically recurring pulses ofrelatively short time duration compared to the recurrence intervalthereof and subject to spurious pulses of a similar nature is combinedwith the output wave of an oscillation generator having a free-runningfrequency substantially the same as said synchronizing signal combiningto obtain a periodic wave dependent in waveform upon the phas relationof said oscillation generator and said synchronizing signal. Electricalenergy of said periodic wave is stored in the form of heat energy andthe stored heat energy is utilized to control the frequency of theoscillation generator.

In a particular embodiment of my invention the alternating currentcomponents of the periodic wave are selected and are made to flowthrough a resistive body. The flow of current through this resistivebody generates heat, the magnitude of which varies in accordance withchanges in the phase relation of the synchronizing signal and theoscillation generator. The heat generated in the resistive body isutilized to control the frequency of the oscillator. In one form of theinvention the heat generating resistive body is located contiguous to afrequency determining capacitive element of the oscillator, thecapacitive element having a temperature coefficient of the properpolarity to maintain synchronism between the oscillation generator andthe synchronizing signal.

The novel features which are considered to be characteristic of myinvention are set forth with particularity in the appended claims. Myinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawings wherein Fig. 1 is a circuitdiagram of a synchronized oscillator system embodying my invention; Fig.2 is a circuit diagram of a synchronized oscillator system embodying myinvention in modified form and Fig. 3 is a circuit diagram of asynchronized oscillator system embodying my invention in an additionallymodified form.

Referring generally to Fig. 1, there is represented schematically asynchronized oscillator arrangement embodying my invention in apreferred form. An oscillation generator indicated generally at isutilized to provide a saw tooth output wave which is amplified in a sawtooth waveform amplifier indicated generally at 2. Pulses which appearacross the output circuit of amplifier 2 are connected to the controlelectrode of a mixingv device indicated generally at 3, a source ofsynchronizing pulses also being coupled to the control electrode ofdevice 3 through input terminal 4. A wave which is derived from acombination of the output wave of device 2 and the synchronizing pulsesappears in the anode circuit of device 3 and the waveform of thisderived wave is dependent upon the phase relation of the oscillatoroutput wave and the synchronizing pulses. The direct current componentof the derived wave is blocked by means of a capacitor 5 and the energyrepresented by the alternating current components of the derived wave isdissipated in the form of heat in a resistor 6. Resistor 6 is locatedcontiguous to a frequency determining capacitor 1 of the oscillator I sothat changes in the relative phase relation of the synchronizing pulsesand the output wave of the oscillator produce a corresponding change inthe alternating current energy being dissipated as heat by resistor 6.This change in heat energy changes the capacity of capacitor 1, thiscapacitor having the proper polarity of temperature coefficient to varythe frequency of the oscillator so that the oscillator is maintained insynchronism with the synchronizing pulses.

Referring now more particularly to Fig. l, the oscillation generator Icomprises an electron discharge device 8 having an anode 9, a controlelectrode I0 and a cathode I I. The anode 9 of device 8 is connectedthrough winding I2 of a transformer I21; and a resistor l3 to aunidirectional source of potential indicated by the numeral A capacitorI5 is connected from the junction point of inductance I2 and resistor |3to ground. The cathode I I of device 8 is connected to ground. Thecontrol electrode H] of device 8 is connected through another winding||i of transformer |2a to a parallel combination comprising capacitorsand I1 and variable resistor |8. Oscillations produced by device 8 arecoupled through a capacitor l9 to the control electrode 29 of anelectron discharge device 2|. A leak resistor 22 connects controlelectrode 20 to ground and the cathode 23 of device 2| is connected toground through a parallel combination of a resistor 24 and a capacitor25. The anode 26 of device 2| is connected through the primary 21 of asweep output transformer 28 to a unidirectional source of potentialindicated by the numeral 29. The screen electrode 30 of device 2| isalso connected to the unidirectional source of potential 29. Thesecondary 3| of transformer 28 is connected to the magnetic scanningcoil which surrounds the neck of the cathode ray tube, indicated as theinductance 32. One side of the scanning coil 32 is connected to ground,the other side of this coil being connected through a limiting resistorand a capacitor 34 to the control electrode 35 of an electron dischargedevice 38. The cathode 31 of device 36 is connected to ground. A leakresistor 38 connects control electrode 35 to ground. A synchronizingsignal may be applied to control electrode 35 through a capacitor 39 anda limiting resistor 40. The anode 4| of device 36 is connected through aresistor 42 to a unidirectional source of potential indicated by thenumeral 43. The anode 4| is also connected through a capacitor 5 toresistor 6 which as mentioned heretofore is located contiguous tocapacitor 1. While there are obviously many ways in which resistor 6 maybe placed in contiguity with the frequency determining capacitor 1, Ihave found it quite convenient to utilize a small tubular--shaped carbonresistor as resistor 6, and a hollow tubular ceramic capacitor ascapacitor 1, the diameter of the resistor being small enough so that theresistor may fit into the central opening of the tubular capacitor. Ifdesired, a small capacitor C indicated in dotted lines in the drawingmay be connected between capacitor 5 and inductance IE to provide somemeasure of direct synchronization as will be discussed in more detailhereinafter. a v p Considering now the operation f'the oscillatorsynchronizing system just described; "the "means for generatingoscillations isshowii as a blocking' oscillator "of well knowndesign.'Brleflycom sidering the operation "of'the blocking oscillator, theanode 9 and control electrode l ordevi'ce 8 are coupled together bymeans of ironcore reed-back transformer 12c so as'to produceoscillations, the control electrode biasingjnetwoi k comprising resistor'18 and capacitors 1' and*""|l being 'su'fliciently largethatoscillation ceases after a single'tcycle thereof'randdoes' not startuntil ala'pse of -anappreciable time interval. i The blocking action ofdevice 8 is accomplishedpy the flow of control electrode" currentthrough capacitors land 11 during the positive portion of the singleoscillation. This "charges the 'capacitorsto a potentialconsiderably'greater than the" control electrode cutoff "potential" ofdevice 8; and the device remains inactive for a period determined 'by'the time "required'ror capacitors 1 and IT to discharge throughresistorI8unti1 device 3- is again'in a conductive stage, whereupon the cycle'is-repeated. Thus'fthe anode'current ofdevice 8 is in the formofa'series of periodic pulses, the recurrence interval of these ulsesbeingdetermined" primarily by the capacitors 1 and I! andresistorfl. 'Thefreerunning frequency of the oscillator may be conveniently adjusted'byvarying resistor 18. While I have indicated the frequency determining R.'0. net- Work of the blocking oscillator as being in series with thecontrol electrode-of device 8;it is ohvious that this network' maybej'utilized in "the anode or'cathodecircuit ofdevice 8 and will 'oper-'ate to control 1 the frequency thereof in a similar manner. I

To generate a saw tooth'sweep voltageioi' scanning the cathode ray tubeviewing-"screen; I provide-a capacitor l5 which is chargedffrompotential source 14 through a resistor13. *Pulses of anode current ofdevice 8 operate periodically to 'dischar'g'e capacitor 15 wherebyasaw-tooth wave or voltage is "produced there'across. *The s aw toothvoltagevrav'e produced across-capacitor iiiis coupled to the control'-elctrode"ofsweep amplifier 2! wherein it is amplified and is transformed in swee output 'transforin'ei 2B into-a saw tooth Wave of currentwhich" flows through electromagnetic scanning coil 32." During'retraceintervalsof the scanning wave there-are produced across scanning coil 32pulses or relatively-large amplitude, these pulses beingproduced byvirtue of the high rate of change of current through the inductance ofthe scanning coil during retrace intervals, as will be readily apparent"to those skilled in the art.

In order to'obtain an electrical wave-which is dependent upon'thephaserelationshippf oscillation generator I and anincoming-synchronizing' signal consisting of periodically -recurrinsynchronizing pulses, I provide-meansfor combining the oscillatorderived outpuh'p'ulses which are produced across scanning 0011 32 andthe incoming synchronizing pulses. More particularly, theoscillator-derived pulses" and the synchronizing pulses are applied tothecontrol electrode of a mixer device 36, wherein'they are combined andamplified. Inthe anodeelrcuit of device" '35 there is'deiived-a wavewhich is dependent in waveform upon the relative phase relation'of theoscillator derived pulses and'the synchronizing pulses. Specifically,inthe-'i1lus-,

trated embodiment, the oscillator derived pulses and'itlie synchronizingpulses are of negative polarity and are or sufficientl'y large amplitude:so that either setof ulses drives the rnixerdevice 38-byond the anode.current cutofi' point,- so that yariatioiisifi the afl'ifil'itud'e or'ithergroup of pluses-ido affect the Waveform of the ,wave derived-fromthe anode circuit of the mixer. There thus. produced in the anode:circuit of mixer device 36 periodically recurring" pulses which.correspond tdtne oscillator derived. pulses and "the synchronizingpulses, these; eriodical-1y recurring pulses bei'ng vvariab'le in widthin accordance with variations the phase relationship ofv theoscillator". derived pulses and the synchronizingipulses.

"Tdcontroi'the oscillatiomgenerator' I in: accordancewith the phaseresponsive wave derived from the anode oi'imixei" device '36, Iprovi'demeans for" supplyingthe alternating current components of said derivedwave to a heat dissipative body whichis located "contiguous to afrequency determining. element "of the oscillationgenerator. Moreparticularly, the alternating current components are passed by blockingca acitor 5" and are applied to a heat dissipative'resistor 6' whichisblocated contiguous "to aitfrequency determining capacitive element" 10i oscillation/generator I. The fio'w of the alternatingcurrent-components of the phase responsive derived wave through resister8 produces heattherein and'the amount of for-compensatingthe-pscillatorfor changes-in heat"dissipated' in resistor S'by such'fiowof current is' dependent'upon'thewaveform of the derived wave. i Theheat produced 'by resistor 6 changes the operating temperature ofcapacitor T'due to the close proximity "of the'two'elements and thechange in temperature" produces a certain"'changein the capacity ofcapacitor 1 depending upon the polarity and magnitude of the temperaturecoefficient "01 the capacitor. Therefore, if" capacitor 1' is chosen"with "the "proper polarity. of temperature *coetiicient; changes inthe'heat' dissipated 'by' resistor- 6 cause corresponding changes infthecapacity of capacitor 7 in the proper direction so as to maintain syn- Jchronismbetween-the-oscillation generator l and thes'ynchro'nizing*p'ulses. For example, if the free running frequency "of oscillationgenerator I is somewhat lowerthan'the'trequency of-the-synchronizingpulses; and the phase displacement s duetothisdifierencein frequencyresults iii-an increase in *the "alternatingcurrent components of thederivedwave-supplied toresistor 6, capacitor 1- would'be chosen with anegative temperature' co'efiicient so that the increased heat dissip'ated by "resistor Gwould" decrease the capacity of capacitor 1and-thus increase the: frequency of oscillation-generator I. If'thefreerunningfrequencyof oscillation generator I were adjusted to a valuehigher than' that oi the synchronizing pulses arr-opposite effect wouldberequired.

l Inasmuch asthe frequency of oscillation generator l ls-controHedbyachange in temperature of one of the" frequency determining elements ofthe oscillator; it-is" desirable-to provide means ambient temperaturewhich are not due to the controllingheat energy. This change in ambienttemperature may be due to dissipation of A heat in other resistiveelements of the'oscillator or to other circuits of the receiverfij'Tocompensate for such changes in ambient temperature Iprovide a'capa'citor I! which is also a frequency determining element 'oi 'theoscillator; and the temperature coefilcient orcapacitor ll is-chosenwith a polarity which is opposite to that of capacitor 1. The capacityof capacitor I! thus compensates for changes in the ambient temperatureof the oscillator so that the only changein the frequency of theoscillator is due to theheat generated by the phase responsive wavewhich flows through resistor 6. While I have indicated capacitor I! asbeing in parallel with capacitor I, it is obvious that the twocapacitors. could be placed in series and the same operation. would beobtained. Also, in order to obtain the maximum simplicity of design, thetemperature coeflicient of variable resistor I8 may be utilized tocompensate for changes in the ambient tern-- perature of the oscillator,thus eliminating the necessity for the additional compensating capacitorI1.

To augment the control afforded by heat dissipative resistor 6, I alsoprovide means for applying the synchronizing pulses directly to the os--cillation generator. Such means comprises a. capacitor C which is shownin Fig. 1 as connected between the capacitor 5 and capacitor 1.Capacitor C is preferably of a relatively small value so thatsynchronizing pulses which are applied. to the oscillator throughcapacitor C do not completely control the oscillator but instead themain controlling effect is obtained by the change in. heat dissipated byresistor 6.

It is an important feature of my invention that the heat energy producedin resistor 6 is stored therein over a substantial number of cycles. Dueto the thermal inertia of resistor 6 there is produced an integratingeffect which averages out any abrupt changes in the alternating currentcomponents which may be due to noise or other spurious and undesiredpulses which are interspersed with the synchronizing pulses. There isthus obtained an essentially noise-free synchronizing system in whichsynchronizing pulses and oscillator derived pulses are combined toobtain a phase responsive derived wave. The alternating currentcomponents of the derived wave are transformed into heat energy andstored in a body having substantial thermal inertia, thereby obtainingan averaging effect over a substantial number of synchronizing pulses.It is to be noted that the heat dissipative body, specificallyillustrated as resistor 6, has a heat time constant which is similar tothe electrical time constant of the resistance-capacitance network whichis utilized in conventional automatic frequency control systems toobtain integration of a phase responsive derived wave. This heat timeconstant may be thought of as the time required for a heated body todecrease in temperature to 1/42 of its initial value with respect to theembient temperature in much the same way as the time constant of aresistance-capacitance network would be the time required for thevoltage across the capacitor to decrease to 1/e of its initial value. Ablack body would thus have a relatively short heat time constant ascompared to a white body. Resistor 6 may be chosen with a heat timeconstant comparable to the electrical time constant of the conventionalautomatic frequency control system in order to produce sufficientintegration so that the synchronization is substan-. tially unaffectedby undesired noise pulses.

Fig. 2 is a circuit diagram of a modified form of my invention which isbasically similar to the oscillator synchronizing system of Fig. 1,identical circuit elements being designated by the same referencenumerals and analogous circuit elements by the same reference numeralsprimed.

In the modification of Fig. 2 a resistor 44 is connected betweencapacitor 5 and ground and a parallel combination of a resistor 45 andcapacitor 46 is connected across resistor 44. In other particulars thecircuits of Figs. 1 and 2 are essentially the same, it being understoodthat the remainder of the circuit not shown in Fig. 2 may be identicalto that of Fig. 1. 7

Considering the operation of the modified form of my invention thusdescribed, a temperature sensitive resistance is herein used as thefrequency determining control element of the oscillator instead of thefrequency determining capacitive element utilized in Fig. 1.Specifically, resistors 44 and 45 are chosen with the proper polarity oftemperature coefficient so that changes in the heat generated thereindue to a flow of the alternating current components of the phaseresponsive derived wave appearing at the anode of device 36, cause thefrequency of the oscillator to vary in the proper direction so thatsynchronism is maintained. A large capacitor 46 is connected acrossresistors 44 and 45 to bypass the alternating current voltage whichappears across these resistors so that a very small portion of thesynchronizing pulses is applied directly to the oscillator. It will beapparent that the incomplete by-passing action of capacitor 46 operatesin a manner similar to the coupling capacitor C of Fig. 1 to provide asmall amount of direct synchronization. Resistor I8 may be varied toadjust the free runnin frequency of oscillation generator I, thesynchronizing control means being efiected through heat responsiveresistors 44 and 45. It is to be noted that the frequency of oscillationgenerator I may be controlled by the bias voltage to which its controlelectrode I0 may be returned in any well known manner. Resistors I8, 44and 45 all carry the direct current component of the control electrodecurrent of the oscillator. The bias voltage for the control electrode I0is thus dependent upon the resistance included in the control electrodecircuit, the resistance of resistors 44 and 45 in turn being controlledby the heat applied thereto. Thus, the bias voltage for the controlelectrode I0 and correspondingly th frequency of oscillator I iscontrolled by the heat applied to resistors 44 and 45. It will beunderstood that pulses which are derived from oscillation generator Iand the synchronizing pulses are applied to the control electrode ofdevice 36 in a manner similar to that shown in Fig. 1.

Fig. 3 is a circuit diagram of an alternative embodiment of my inventionwhich is essentially similar to the synchronizing system of Fig. 1,identical circuit elements being designated by the same referencenumerals and analogous reference elements by the same reference numeralsprimed, except that the means for generating oscillations comprises inthe present arrangement a sine wave oscillator. This oscillator, whichmay be of any well known type, is shown as a cathode tap Hartleyoscillator in which the cathode I I of electrode discharge device 8 isconnected to a tap 41 on inductance 48. A capacitor 49 is connected inparallel with inductance 48 to form a parallel resonant tank circuitwhich is resonant at the desired oscillation frequency. A biasingnetwork comprising capacitor 50 and resistor 5I is connected to thecontrol electrode of device 8.

In considering the operation of the e1nbodiment of my invention shown inFig. a phase responsive derived wave is produced at the anode 4i ofdevice 36. The alternating current components 9 eof this derivedwaveform are coupled throu'gh capacitor toa heatgene'ratin'gresistor 6.The heat generator resistor 6 is located contiguous to the frequencydeterminingcapacitor ofz the Hartley oscillator-L Thus; changes the-:heat generated by resistor 6 produ'ces corres'ponding changes in the:capacity-of-=capacitcrlili This capacitor is chosen'Withatemperaturecoefllcient of the proper polarityto maintain synchronismbetween the incoming synchronizing pulses and the oscillationgenerators" It wurbe understood that-pulses of anode current ofdevice'll op'era'te periodically to discharge capacitor I5 whereby a sawtooth wave ofvoltage-is produced across cae pacitor 5| inL-a mannersimilarto that -ofthe blocking oscillator Of FigE L- While' lT haveindie' cated' the sine wave oscillator as being ofthe Hartley type; it"will bereadily apparent-to those skilled in the art'that other typesofs'ine wave oscillators may be utilized witho'ut distinguish ing from myinventions It i's alsdpossibllatoicom trol the inductance element =ofth'e' sine 'wave cs cillator by means of th'e-heatmontrol i'esistorfi.

From the above desoriptionpf the inventionit will be evident thatanoscillationsynchronizing system embodying my invent-ion has theadvantage that synchronization is'obtaine'd fromth alternating currentcomponents -of a 'phase're sponsive derived Waveform, these-componentsbeing integrated overa substantialnumberofiic'ycles by virtue oftheheat-timeconstantofa heat dis sipative bodyI It is 4 thus *possibleto' utilize'a synchronizing 'signa'l wliich is interspersed withspurious and undesired-pulses-of substantial-am plitude and still obtainessentially nolse 'free synchronization of the oscillator. Further,since the integration may be 1 effected thermally ina =con-'"ventionally sized resistor the circuit becomes con siderably simplerthan :tliat 'of [automatic-fre quen'cy control systemsimwhich 'aunidirectional control volta'ge is obtainedbythe use ofauxiliaryrectifiers and amplifier-s:

Whilethe inventiorrhas been'-describd-bypar-' ticular embodimentsthereof-pf it "will-' be'--'under'-- stood that numerous modificationsmay be made by those skilled inthe art without departin'gfro'rn theinvention. I therefore aim in'the'app'ended claims to cover all such"equivalent-variations as come within the true spirit-andscope of myin-"J;

vention. v

What I claim as new'and desire to secure'by' LettersPatent of the UnitedStates is:

1. Ina televisionare'ceiver adapted to. receive synchronizing signals'.consistir'igiof' periodically," recurring pulses of shortitimedurationcompared.

to the recurrence interval thereof and subject "to spurious pulses of asimilar nature'fan oscillator synchronizingsystem "comprising anoscillation generator forgeneratinga periodic outputwave ofapproximatelythe same average frequency as said synchronizing-signalsintheabsence of frequency-corrective energy applied thereto; said"frequencyof --"sa-id oscillation-- generator in the properdirectionsubstantially to 'maintain I the output Waveof-said generatorinpha'se with said synchronizing signals.

2. a television-receiver adapted'to receive synchronizing-signalsconsistingof periodically recurring pulsesof showtime-duration comparedto the-recurrenceintervalthereof and subject to spurious noise" voltagesof a similar nature; an oscillator synchronizing system comprising anoscillatoihaving-a free running frequency substantially .equal to thefrequency of saidsynchronizingsignals," said oscillator having atemperature responsivefrequeney determining element asso-' ciated-th'rewithf a heat dissipative" element ad'- jafoent saidfrequencydetermining element, means for-obtaining output pulses fromsaid oscillator whichareofrelatively" short time durationcom=pared"to'-"the recurrence interval'thereof, means for combining saidsynchronizing signals and said proper direction substantially tomaintain said output pulses in phase with said synchronizingv signals: I

3.Iri"a television receiver adapted to receive synchronizing signals"consisting of periodically" recurring" pulses-"of short time durationcompared to therecurrenceinterval' thereof and subject to spurious noisevoltages "of a similar nature, an oscillat'or synchronizing systemcomprising an 0s cillator havinga free running frequency substantiallyequal-tothe-frequency .of said synchronize ing-signalsi'said oscillatorhaving first and second temperature-responsive frequency determiningelements associated therewith; a heat dissipative element incontiguitywith said first frequency determiningelement, means for obtaining outputptilssfrbm'said oscillator which are of relative- Iy shOrt time durationcompared tothe recurrence interval -thereof,uneans' for combining saidsynchronizingsig'nalsand said output pulses to obtainderivedpulsesoftrelatively fixed amplitude;

the width of saidi'derived'pulses being dependent, upon} therelativephase relation of said synchro-. mzing pulsesand-saidfoutput"pulses, means for,

selecting {the alternating: current components of '-said'-derivedpulses; means for supplying said alternating"'current'components to saidheat-dissipiattive element;- said first 'frequencydetermin-1ng-"element*having"a temperature coefficient of such polaritysaid-heat" dissipative element cause changesin the frequencyof'saidpscillator*in the proper direc-,

non-"substantially :to maintain said oscillator in phas'e withsaidsynchronizing signals, said sec.-

ondf-requen'cydetenniningelement havinga tem-- perature 'coefiicient of.a polarity opposite to said first frequency determining elementwhereby:

changes'jin ambient temperature have substan tially no effectl'upon thefrequency of said os-'- 4; an oscillator. synchronizing system', thecombination of-:a source of synchronizing signals i that changes in thetemperature of output wave of substantially the same frequency as saidsynchronizing signals in the absence of frequency-corrective energyapplied thereto, a resistor in contiguity with said frequencydetermining capacitive element, means for substantially eliminating thedeleterious effect of said spurious and undesired impulses whilemaintaining synchronism between said synchronizing signals and saidoutput wave comprising, means for deriving a periodic wave dependent inwaveform upon the relative phase relation of said synchronizing signalsand said output wave, means for selecting the alternating currentcomponents of said periodic wave, and means for applying said selectedalternating current components to said resistor. said capacitive elementhaving a temperature coefficient of capacity of such polarity thatchanges in the temperature of said resistor cause changes in thefrequency of said oscillation generator in the proper directionsubstantially to maintain said output wave in phase with saidsynchronizing signals.

5. In an oscillator synchronizing system, the combination of a source ofsynchronizing signals which may be contaminated by spurious andundesired impulses, an oscillation generator having atemperature-sensitive frequency determining element and arranged toprovide an output wave of substantially the same frequency as saidsynchronizing signals in the absence of frequencycorrective energyapplied thereto, a resistor in heat-transmitting relation to saidfrequency determining element, means for substantially eliminating thedeleterious effect of said spurious and undesired pulses whilemaintaining synchronism between said synchronizing signals and saidoutput wave comprising, means for deriving a periodic wave dependent inwaveform upon the relative phase relation of said synchronizing signalsand said output wave, and means for applying only the alternatingcurrent components of said derived wave to said resistor, said frequencydetermining element having a temperature coefficient of such polaritythat changes in the temperature of said resistor cause changes in thefrequency of said oscillation generator in the proper directionsubstantially to maintain said output wave in phase with saidsynchronizing signals.

6. In an oscillator synchronizing system, the combination of a source ofsynchronizing signals which may be contaminated by spurious andundesired impulses, an oscillation generator having atemperature-responsive frequency determining element and arranged toprovide an output wave of substantially the same frequency as saidsynchronizing signals in the absence of frequencycorrective energyapplied thereto, a heat dissipative element adjacent said frequencydetermining element, means for substantially eliminating the deleteriouseffect of said spurious and undesired impulses while maintainingsynchronism between said synchronizing signals and said output wavecomprising, means for deriving a periodic wave dependent in waveformupon the relative phase relation of said synchronizing signals and saidoutput wave, and means for applying only the alternating currentcomponents of said derived wave to said heat dissipative element, saidfrequency determining element having a temperature coefficient of suchpolarity that changes in the temperature of said heat dissipativeelement cause changes in the frequency of said oscillation generator inthe proper direction substantially to 12 maintain said output wave inphase with said synchronizing signals.

7. In an oscillator synchronizing system, the combination of a source ofsynchronizing signals which may be contaminated by spurious andundesired impulses, an oscillation generator having a temperaturesensitive frequency-determining element, said generator being arrangedto provide an output wave of substantially the same frequency as saidsynchronizing signals in the absence of frequency-corrective energyapplied thereto, means for substantially eliminating the deleteriouseffect of said spurious and undesired impulses while maintainingsynchronism between said synchronizing signals and said output wavecomprising, means for comparing said output wave with said synchronizingsignals and deriving therefrom a periodic wave dependent in waveformupon the relative phase relation of said synchronizing signals and saidoutput wave, and means responsive to the alternating components of saidderived wave for varying the temperature of said element as a functionthereof, said element having a temperature coefficient of such polaritythat changes in the temperature of said element will vary the frequencyof said oscillation generator in the proper direction substantially tomaintain said output wave in phase with said synchronizing signals.

8. In an oscillator synchronizing system, the combination of a source ofsynchronizing signals which may be contaminated by spurious andundesired impulses, an oscillation generator having first and secondtemperature-sensitive frequency-determining elements and arranged toprovide an output wave of substantially the same frequency as saidsynchronizing signals, a heat dissipative element in contiguity withsaid first frequency-determining element, and means for substantiallyeliminating the deleterious effect of said spurious and undesiredimpulses while maintaining said output wave in synchronism with saidsignals comprising means for deriving a periodic wave dependent inwaveform upon the relative phase relation of said output wave and saidsignals, means for applying only the alternating components of saidperiodic wave to said heat dissipative element, said firstfrequency-determining element having a temperature coefficient of suchpolarity that changes in the temperature of said heat dissipativeelement cause changes in the frequency of said oscillator in the properdirection substantially to maintain said output wave in phase with saidsignals, said second frequency-determining element having a temperaturecoefficient of opposite polarity to said first element to correct forambient temperature changes.

ROBERT B. DOME.

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